The present invention relates to a new and improved construction of thread monitoring apparatus for textile machines.
More specifically, the invention relates to a filling or weft thread monitoring apparatus, particularly suitable for use with shuttleless looms, which comprises a thread feeler encompassing a thread scanner and pivotable relative to the thread. The thread feeler coacts with an electrical circuit arrangement for generating a fault signal. This circuit arrangement contains a measuring cell generating a thread signal and through which there can move the thread feeler as well as a switching stage for comparison of the thread signal with a machine-controlled reference signal.
At thread processing textile machines, such as for instance shuttleless looms, it is necessary to monitor the thread, for instance as to its presence or availability. For this purpose there is used a weft thread-monitoring apparatus of the previously mentioned type at locations of a momentary relative transverse movement between a thread and a machine element, for instance approximately at the region of the reed movement, by means of which the weft thread is beaten at the cloth fell.
With one such type monitoring apparatus, conventionally known in the art as a filling or weft thread monitor, the thread feeler is constituted by a wire bracket fixedly arranged at the weaving reed or the comb or the sley or at the loom. This wire bracket forms part of an electrical circuit for the shutdown of the loom. During the beating movement of the sley the wire bracket moves towards a contact element, and if there is properly present weft thread then the wire bracket is restrained from making contact. On the other hand, if the weft or filling thread is absent, then the electrical circuit between the wire bracket and the contact element is closed by making contact and the machine is shutdown.
Now it has been found for considerable time that such arrangements are not capable of insuring for a positive contact at all points in time, since the wire bracket possesses too little stability for a switching element.
In Swiss Pat. No. 496,121 there has been disclosed to the art an apparatus of the previously mentioned type, wherein a feeler fork is subjected to the positioning pressure of a spring. Hence, the feeler fork contacts the thread with a relatively large acceleration. This requires, however, that the thread at the therein not particularly illustrated warp threads be supported closely to both sides of the individual feeler fork tines, so that the filling or weft threads are not depressed by the arriving feeler fork, and thus, there is produced a pulse at the feeler fork hub by a light barrier interrupter. In this case the smaller the warp thread density that much less useful becomes this arrangement.